1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, that can be used for digital cameras. The present invention also relates to a movable lens hood mounting mechanism of the zoom lens which makes it easy for the movable lens hood to be mounted to, and dismounted from, the zoom lens.
2. Description of the Related Art
A zoom lens, or a zoom lens barrel, having a mechanism for moving a lens group, which is guided linearly along the optical axis of the zoom lens in a predetermined moving manner by rotation of a cam barrel having cam grooves, is known in the art. In such a conventional zoom lens, it is often the case that the cam barrel itself also serves as an external component of the zoom lens or as a support member which directly supports an moveable external barrel of the zoom lens. Due to this structure, the cam barrel has a tendency to be influenced by external forces applied to the cam barrel. Nevertheless, such a cam barrel has no substantial adverse effects if the cam barrel is used an element of the zoom lens of a conventional camera using light-sensitive film such as 35 mm or APS compact zoom camera.
However, such a cam barrel does have substantial adverse effects if the cam barrel is used as an element of the zoom lens of a digital camera because object images are formed on the sensitive surface of a small CCD (CCD image sensor) which is much smaller than the picture plane of conventional cameras using light sensitive film. Namely, upon assembly, every lens element of a digital camera must be optically centered, correctly spaced, and held firmly with a fairly high precision, e.g., tens times greater than that required in conventional cameras using light-sensitive film. For instance, if the angle of view is constant, the focal length of a photographing lens becomes shorter as the size of the picture plane reduces, which in turn reduces the sizes of all the elements of the photographing lens such as lens elements, lens frames and other elements. Therefore, the influence that a tolerance (e.g., 10 μm) has on a photographing lens system of a digital camera is much larger than the influence that the same tolerance would have on a photographing lens system of a conventional camera using light-sensitive film. Accordingly, manufacturing error which falls within tolerance of optical performance in the photographing optical system of a conventional camera using light-sensitive film can be outside the tolerance of optical performance in the photographing optical system of a digital camera.
Accordingly, there is a high possibility of a conventional cam barrel, which is disposed at a position where the cam barrel is easily influenced by external forces, deviating from its original position in the optical axis direction of the photographing lens, or being eccentric or tilting relative to the optical axis of the photographing lens. Such an error in the conventional cam barrel has influence on one or more lens groups which are engaged with cam grooves formed on the cam barrel. Consequently, the optical performance of the photographing lens deteriorates.
Concerning another matter on zoom lenses, in a zoom lens whose angle of view varies in accordance with a variation of the focal length, unwanted light is preferably prevented from falling on the lens surface in accordance with a variation of the angle of view. However, a zoom lens having a lens hood which can vary the maximum incident angle of light to the lens surface in accordance with a variation of the angle of view is not known in the art.